Interaction of saponification products of Robinia pseudoacacia seed oil with cetyltrimethyl ammonium bromide

The interaction between novel saponification products (RCOONa or RCOOK) of Robinia pseudoacacia seed oil and cetyltrimethyl ammonium bromide (CTAB) in aqueous solution have been investigated by surface tension method at 25°C. The critical micelle concentration (cmc) of RCOONa/CTAB and RCOOK/CTAB mixture were measured. The surface properties of saponification products, CTAB as well as the mixed system were explored and compared. The composition, activity coefficient of mixed micelle, and the interaction parameters (β^σ, β^M) between surfactants were estimated according to the Regular Solution Theory, the Clint's model and the Rubingh's model in the framework of pseudophase separation model. The experimental results suggested that both RCOONa and RCOOK have synergism with CTAB in mixed micelle formation and surface tension reduction through calculating of β^σ and β^M in the mixed system. This could be attributed to the strong interaction between the head groups with opposite charges in the surfactant molecules.